Selective signaling system



April 28, 1936.

c. s. DEMAREST SELECTIVE SIGNALING SYSTEM Filedfict. 13, 1932 EQES wanShaun; MW

T INVENTOR C. 5. Den Lowest BY v ATTORNEY Patented Apr. 1936 PATENTOFFICE SELECTIVE SIGNALING srs'mu Charles "Sidney Demarest, Ridgewood,N. J., as

signor to American Telephone and Telegraphv Company, a corporation ofNew York Application October 13, 1932, SerlalNo. 637,650 3 Claims.wr'm-sas) This invention relates to-electrical circuits, and moreparticularly to circuits for selecting signaling or switching, in whicha signal may be transmitted selectively'to one of a plurality ofcircuits or a circuit may be connected selectively to one of a pluralityof, circuits.

Such arrangements have heretofore been provided by the use ofelectromagnetically operated relays or selector switches, involvingmechanical motion of some parts thereof. These moving parts haverequired careful adjustment and maintenance and troubles have also beenexperienced at the points of electrical contact as films of dirt orcorrosion may impair the electrical contact to such an extent that thecircuit becomes noisy or actually is not completed. It is an object ofthis invention to provide means whereby such selective switching orsignaling operations may be carried out without the use ofelectro-mechanical devices such as relays or selectors. I have describedsuch a system in my copending application, Serial No, 629,382, filedAugust 18, 1932, Patent No. 1,908,326, from which this invention isdifferentiated by the method of selection employed. In the abovementioned application, selection is made by the use of a train of codedimpulses. In this inventiomhowever,

I have utilized electrical tuned circuits, together with a sourceofsignaling current of adjustable frequency, so that by sendingcurrentpf a ticular frequency one of a plurality or circuits isselected. Obviously, it would be possible to combine the features ofthis invention with that already referred to so as to increase thenumber of stations or circuits available for selection, the

first selection being made by selecting the proper frequency, afterwhich "coded impulses of this frequency select a particular circuit fromthe I. indicatesthe subscribers station and its associated lineconductors 2 and 3, connecting it to the gas-filled tube switchingequipment at the central oflice. Tubes 4" and 5 are so -arranged thatline conductors 2 and 3 are normally connected to the conductorsSB and96 of line 0 through the arc paths of these tub'es. Grid batteries 1 forthese two tubes are poled so that the established. Thus if none of thekeys Ki are operated, a cbnnection may be established'between thesubscribers station I and an operator over lines 96 and 96'. Signalingimpulses are sent from keys K; to KN over conductors 21 and 28,. thecurrent for such impulses being supplied 5 by the vacuum tube oscillatorcomposed of vacuum tube 30, output transformer 29, conmined frequency tobe transmitted over signal ing pairs 2'! and 28. Obviously theseconductors 21 and 28 might be the same conductors as 2' and 3,separation of the selecting currents from the iiiother currentstransmitted over conductors 2 and 3 being made by proper choice ofselecting frequencies and the provision of suitable filters. An untunedtransformer I8 is connected with-its primary bridgedacross the signalingpair and 2d its secondary connected to the grid and cathode ofgas-filled tube}, IS. The grid ofthis tube is normally biased negativelyby battery' I I. It should be noted that the same reference characterhasbeen used for batteries, coils and the like as of id entical functionassociated with different pa of the circuit. Upon the application of anysig "a1ing current of frequency F1 ,to Fn, an arc will be establishetube l9. Upon'the striking of this arc, current will flow from"alternator 22 10 to the primary of transformer 16. Current will flowfrom the secondary thereof through theprlmaries of transformers-l3 andin. parallel, over conductors l6 and I5, through condenser 2|,

anode of tube l9,'th1f0ugh the arc to the cathode, 35 I and thencethrough condenser 20 back to the secondary of transformer l6. {thesecondaries of transformers l3 and M are connected to the rectifierresistance units II and I2 in the-"anode;

circuits of tubes 4 and 5. These rectifiers areiso 40- poled that theresulting electromotive force across the resistance elements will'opposethe anode batteries 8 and extinguish the arc in the tubes 4 and 5, thusdisconnecting line 0. Choke .coils l0 and resonant circuits 9 keep thealternating/1i current from generator 22 out of the transmission circuitover conductors 2 and 3. At the same time the signaling current appliedover conductors 21. v and 28, which is of one of N predeterminedfrequencies F1 to FN will actuate the corresponding 50 set of connectortubes, of whichonly one set,

' the F1 group, has been indicated in the drawing.

Supposing that the frequency sentout is'Fi, due, to operation of key K1at thestation,thecondepser C1 will be connectedto the oscillator coil 3l and 0111- 55 i rent of frequency F1 will be applied to conductors 21and 28. This current will be passed by selective network 32, butrejected by all others. As a rest'rit, in addition to quenching tubes 4and 5 as hereinbefore explained, alternating current from vacuum tubeoscillator 30 will be applied to the primary of transformer 33 and thevoltages induced in the secondaries of this transformer will cause arcsto be established in gas-filled tubes 34 and 35, the positive halfcycles being suificient to override the effect of biasing batteries 11.When the arcs have struck it is apparent from the drawing that a circuitis established from conductors 2and 3 to conductors 52 and 52 of line I.

If another key, say K3, be now pressed, a double connection toibothlines I and 3 would be established. If, however, it is desired .toestablish another siiTgle connection, key KN must first be op- I eratedsending out frequency Fa. It will be apparent that tube 42 will beoperated, as voltage of this frequency Fa will be applied to the grid oftube 42' through selective network 40 and transformer 4|. Direct currentwill flow from battery 3 through inductance 5|, resistance 45 to theanode'of tube 42, through the arc thereof and back to battery 8. At thesame time an A. C. path from generator 50 will be completed through theprimary of transformer 49, condenser 48, the arc path of tube 42 andback to generator 50. Alternating current will flow from the secondaryof transformer. over conductors 25 and 25, to rectifier resistancenetwork 24, and will after rectification build up a direct potentialopposing the anode battery of tube l9, thereby quenching this tube andpermitting gas-filled tubes 4 and 5 to' again establish an arc, thusrestoring the connection to'line 0. 'At the same time alternatingcurrent will flow from conductors 25 and 26 into the primaries oftransformers 38 and 39. The anode circuits of the connector tubes 34 and35 contain rectifier and resistance elements 36 and 31, connected to thesecondaries of transformers 38 and 39. The direct potential builtup'a'cross the resistances of these rectifier-resistance units willoppose the anode batteries of tubes '34 and 35 and thus quench the arcstherein, so disconnecting conductors 2 and 3 from line I.

At the same time transformer 41 has supplied an A. C. potential torectifier 43, and this will slowly charge up condenser 46, throughresistance 44, and in such a manner as to oppose the voltage of theanode battery 8 of'tube 42. After a period predetermined by theamplitude of the I voltage supplied from the secondary of translpossible. 5-

former 41, the'values of resistances 44, 45 and of capacity 46, thisvoltage will be sufficient together with the potential of the negativehalf cycles of the alternating voltage to' quench the arc in tube 42.The system is thus restored completely to its normal condition.

It isobvious that conductors 21 and 28 could be made the same asconductors 2 and 3 as above stated by providing additional filtering.If'this is done, the signaling current from generator 30 may be appliedto the circuits 0, I, etc., selected on a frequency basis. If now theseline conductors be arranged to serve as the input circuit to a selectivesystem of the-type shown in my above identified patent, and if pulsesofthe frequency sent out by generator 30 be sent, instead of a singlesignal, selection of further lines maybe made on' a coded impulse basis,making it pos- While this invention has been" described with regard to aparticular embodiment thereof, it is not to be regarded as limited tothe specific arrangements disclosed, but includes any and allorganizations falling within the scope and spirit of the appendedclaims.

What is claimed is:

1. In a signaling system, selectively operated switching meanscomprisin'ga plurality of gasfilled tube devices each having input andoutput circuits, each of said devices having plate voltages suflicient'to maintain the devices in discharging condition after they areinitially broken down and started in discharging condition,extinguishing means associated with the output circuits of each of saidtube devices for changing said plate voltages so that they will beinsufiicient to maintain the devices in discharging condition, the firstof said gas-filled tube devices being normally adjusted to be in adischarging condition, filtering devices adapted to transmit differentfrequencies associated with the input circuits of all of said tubedevices except said first tube'device, a multifrequency source,switching means for applying currents of different frequencies from saidsource to said filtering devices to selectively cause the discharge ofsaid tube devices, means directly controlled by any of the currents fromsaid source for operating the extinguishing means associated with saidfirst gas-filled tube device-switching means for v applying current of adefinite frequency from said source to the last one of said gas-filledtube devices to cause the operation of said last tube device, and meanscontrolled by the operation of said last tube device for operating theextinguishing devices associated with filled tube devices each havinginput and output 40 circuits, each of said devices having plate voltagessuflicient to maintain the' devices in discharging I, condition afterthey are initially broken down and started in discharging condition,extinguishing means associated with the output circuits of each of saidtube devices for changing said plate voltages so that they will beinsufiicient to maintain the devices in discharging condition, the firstof said gas-filled tube devices beingnorinally adiusted to be in adischarging condition, filtering devices adapted to transmit differentfrequencies associated with the input circuits of all ofsaid tubedevices except said first tube device, a multifrequency source,switching means for applying currents of different frequencies from saidsource to said filtering devices to selectively cause the discharge ofsaid tube devices, means directly controlled by any of the currents fromsaid source for operating the extinguishing means associated with saidfirst gas-filled tube device, switching" means for applying current of adefinite frequency from said source to the last one of said gas-filledtube devices to cause .the operation of said last tube device, meanscontrolled by the operation of said last tube device for operating theexting'uis g devices associated with all of said tube devices exceptsaid first-tube device, and r slow-operating means associated with andcontrolling the operation of the extinguishing means of said last one ofsaid gas-fi1led tube devices.

3. In a signaling system, selectively operated switching meanscomprising a plurality of gasfilled tube devices each having input andoutput circuits, each of said devices having plate voltages sufiicientto maintain the devices in discharging condition after theyare initiallybroken down and started in discharging condition extinguishing meansassociated with the output circuitsot each of said tube devices forchanging said plate voltages so that they will be insumcient to maintainthe devices in discharging condition, the first of said gas-filled tubedevices being normally adjusted to be in a discharging condition,filtering 'devices adapted to transmit diflerent frequencies associatedwith the input circuits of all of said tube devices except said firsttube device, a multifrequency source, switching means for applyingcurrents of difierent frequencies from said source to said filteringdevices to selectively cause the discharge of said tube devices, anauxiliary gasfilled tube device for controlling the extinguishing meansof said first normally operated gas! said auxiliary gas-filled tubedevice, switching means. for applying current 01. a definite frequencyfrom said source to one of said gas-filled tube devices to cause theoperation of said last mentioned tube device, and means controlled bythe operation of said last tube device for causing the operation of theextinguishing devices associated with said auxiliary gas-filled tube andCHARLES S. DEMARES'I'.

